A stamina test
Five minutes shows whether you can keep a steady rhythm. Keep your wrist floating, fingers on 4, 5 and 6, and your eyes on the numbers.
A full five minute numeric keypad test. It shows the speed and accuracy you can hold, which is what employers want to see.
Keystrokes per hour (KPH) counts every digit and Enter press, scaled to an hour. Net KPH only counts entries you typed correctly, which is what employers usually ask for.
Use the home position (4, 5, 6), never look at the keypad, and practise 5 to 10 minutes a day. Accuracy first, then speed.
Switch to Number row mode to practise the digits above the letters, or plug in a USB keypad.